1. Field of the Invention
This invention is in the field of apparatus for controlling air flow through openings in the side walls of a pressurized plenum chamber, particularly, by a baffle that induces turbulent flow within the chamber, substantially dampens out oscillations in the flow of air within the chamber, and substantially equalizes pressure within the chamber so that there is no significant difference in the rate of flow of air through openings in the side walls of the plenum as a function of the position of the openings along the length of the plenum.
2. Description of the Prior Art
In large electronic systems such as digital data processing systems it is well known to cool the components that produce heat; semiconductor devices, resistors, power supplies, etc. by directing streams of air moving at a relatively high velocity over such devices. With the development of medium and large scale integrated circuits, such circuits are frequently mounted on printed circuit boards which boards are in turn mounted on fixtures, or racks, so that large numbers of such boards are positioned in close proximity to one another to facilitate electrical interconnections between boards. To provide the necessary quantity of air to cool the components mounted on these boards, an air duct, or plenum chamber, closed at one end is mounted in the cabinet in which the circuit boards with their components mounted on them are located. The plenum chamber can be mounted vertically, or horizontally, preferably perpendicular to the planes in which the printed circuit boards lie, and has essentially a uniform cross sectional area along its entire length. Air metering openings are formed in the side walls of the plenum chamber to direct air over the components to be cooled. An air pump provides the cooling air and is connected to the air inlet end of the plenum chamber with the other end of the chamber being closed.
The problem with prior art systems for distributing air to cool components in complex electrical systems is the result of increasing the amount of cooling air to be distributed by the system while maintaining the dimensions of the system, particularly the cross sectional area of the plenum chamber constant. Increasing the amount of air forced into plenum chamber per unit time results in an uneven distribution of air flowing through the metering slots in side walls of the plenum chamber as a function of the distance of such openings from the air pump. The velocity of air flowing through the metering slots at the more distant, or closed, end of the chamber is at a maximum, and at a minimum through the metering slots nearest the pump. The reason for the variations in flow rates through air metering openings of substantially the same size is due to the magnitude and direction of the velocity vector of the air as it enters the plenum chamber. The velocity vector is at its maximum magnitude at the entrance to the chamber and its direction is substantially parallel to the side walls so that the air flows through the air metering openings in the upper portion of the chamber only at a significantly reduced velocity. Near the closed end of the chamber the magnitude of the velocity vector approaches zero as its limit so that air flows through the metering openings in the side walls in the lower portion of the chamber at a maximum rate corresponding to the static pressure of the air in the chamber. In addition the air flow from the air pump, typically a centrifugal blower, does not have a constant velocity profile across the air stream produced. The air stream has a higher velocity center core which tends to bounce, or to be reflected, from the side walls of the plenum chamber so that oscillations, or oscillatory changes in pressure, occur within the chamber. This phenomena further exacerbates the uneven distribution of flow rates through the air metering openings along the length of the side walls of the plenum chamber. The variations in flow rates result in inadequate cooling of some components to the detriment of their reliable performance, particularly over a sustained period of time.